Standing in nothingness before the Big Bang

[marcus]

Space did not exist before the big bang...

How do you know that? How can you be sure? We do not have a scientific consensus that space did not exist before the start of expansion. Older models break down right at the start and can't say anything meaningful---more recent ones do not suffer that kind of breakdown (don't have a "singularity").
The relevant field of research is called Quantum Cosmology. Here's a keyword search of recent professional journal articles on QC if anyone wants to get an idea of what models of start of expansion (no longer always referred to as "big bang") are like. Glancing at some of the titles and abstracts will give a general impression.
http://inspirehep.net/search?ln=en&...search=Search&sf=&so=d&rm=citation&rg=25&sc=0
The search gives 640 quantum cosmology research papers that appeared since 2009 but you can get a reasonable impression just by glancing at the short summaries of the first 10 or 20. In the first 100 or so papers, the most common model tends to be (nonsingular) big bounce.

Hello, I have a question:... Would I first feel the pull of the gravity of the growing universe, then see it's light,...

I think it is perfectly OK how you asked the question. It's clear you are looking for a MENTAL IMAGE OF THE START OF EXPANSION.

Of course it's difficult to imagine actually being there---being in the universe when it was extremely dense and hot and super-packed with energy---and where else could anyone be since the universe is everything that exists? So people immediately start raising PHILOSOPHICAL objections, but all you wanted was a mental image so you could picture it concretely

No picture can be perfect, but here's one for starters. It corresponds to the main bulk of the first 50-100 research papers in that listing of keyword hits I linked.

The Inspire listing contains also contains various OTHER concepts of the start of expansion, but I don't happen to have graphic illustrations of them.

 

[Chalnoth]

The relevant field of research is called Quantum Cosmology.

This is not true. Quantum Cosmology is a subset of the work in this area, these days generally used to specifically talk about the application of the rather speculative Loop Quantum Gravity to a bounce in the early universe.

It's a term that is usually not used to refer to other proposed early universe models, such as the ekpyrotic universe, or the spontaneous inflation of the Carroll-Chen model.

Such models are extremely numerous and diverse, but there isn't a whole lot of active research in this area simply because there isn't very good data to point the way. If we get some significant improvements in data from the early universe (such as detections of primordial gravitational waves), we will probably have a lot more activity in this area.

 

[Swimfit]

Marcus thanks so much for your post it was very informative! Instead of all the critical comments made by others. All I was trying to do was find out in what order things might be felt. Gravity, light and the explosion. I really didn't mean that I could actually stand in nothingness or what ever it might be. But in reality I guess we really can't know. I just wish people would read beyond the original question and read all the treads before commenting. Thanks Marcus for your comment I will reread it and make sure I understand it. Thanks again swimfit

 

[marcus]

Good suggestion Chally! When I use the keyword "quantum cosmology" I get 640 papers (since 2009).
But when I add "ekpyrotic" I get 691 papers!

Actually if you actually look thru the list either way you will see a lot of Non-Loop papers, they just don't get cited so much, so you don't see as many in the top 20 or 30 of the listing. It is sorted by the number of citations.

So I will correct what I had to say.

Older models break down right at the start and can't say anything meaningful---more recent ones do not suffer that kind of breakdown (don't have a "singularity").
The relevant field of research is called Quantum Cosmology. Here's a keyword search of recent professional journal articles on QC if anyone wants to get an idea of what models of start of expansion (no longer always referred to as "big bang") are like. Glancing at some of the titles and abstracts will give a general impression.
http://inspirehep.net/search?ln=en&...search=Search&sf=&so=d&rm=citation&rg=25&sc=0
The search gives 691 quantum cosmology or ekpyrotic research papers that appeared since 2009 but you can get a reasonable impression just by glancing at the short summaries of the first 10 or 20. In the first 100 or so papers, the most common model tends to be (nonsingular) big bounce.

...
No picture can be perfect, but here's one for starters. It corresponds to the main bulk of the first 50-100 research papers in that listing of keyword hits I linked.

The Inspire listing contains also contains various OTHER concepts of the start of expansion, but I don't happen to have graphic illustrations of them.

 

[MathJakob]

Would I first feel the pull of the gravity of the growing universe, then see it's light

You would feel the pull of gravity before you saw light. Understandably people are right when they say your question does not make sense but cmon guys you know what he is asking... Imagine you was standing 100 light years away from the big bang, you're standing in nothingness and the big bang happened, you'd feel the pull of gravity first then 100 years later you'd see the universe.

My answer makes no sense I know as does the question, but it's obvious what the OP is trying to figure out. I think it's just more of a random question as apposed to anything meaningful.

 

[Chalnoth]

You would feel the pull of gravity before you saw light.

?

Gravity propagates at the speed of light.

Understandably people are right when they say your question does not make sense but cmon guys you know what he is asking... Imagine you was standing 100 light years away from the big bang, you're standing in nothingness and the big bang happened, you'd feel the pull of gravity first then 100 years later you'd see the universe.

Well, no. You probably wouldn't see (or feel) anything at all, because this event would look like a microscopic black hole that popped into existence and almost instantaneously decayed. In short, it'd just look like, from the outside, a normal quantum vacuum fluctation that happens regularly all around us all the time, and is therefore indistinguishable from the vacuum.

 

[MathJakob]

Gravity propagates at the speed of light.

Oh yeh! I forgot... but what about the inflation at the start of the big bang? So if gravity propagates at the speed of light and the universe is expanding faster than the speed of light, then are there some parts of space which do not have any gravity?

What would happen if you took the sun and put it in that part of space where there isn't any gravity? (hyperthetically)

 

[Swimfit]

So your saying that at the Big Bang gravity would move as fast as the light? And that gravity would only be felt or sensed first in the fabric of space time? Now the sun thing would the sun stay there without the fabric of space time or continue to move?

 

[Swimfit]

So is there gravity without mass? Or does the mass create the gravity?

 

[Drakkith]

So your saying that at the Big Bang gravity would move as fast as the light? And that gravity would only be felt or sensed first in the fabric of space time? Now the sun thing would the sun stay there without the fabric of space time or continue to move?��

Changes in the metric of spacetime move at the speed of light. A typical example is a gravitational wave. I'd prefer not to talk about what was felt or seen first, as the very early universe does not quite work the same way as it does now. Forces were unified and radiation was so energetic that it could create matter and antimatter. Not to mention that we don't even know how the origin of the universe happened.

Also, talk of what would happen without the fabric of spacetime makes no sense. Without spacetime there is nothing. No dimensions, no anything.

So is there gravity without mass? Or does the mass create the gravity?

Mass and energy cause spacetime to "bend", which usually manifests as an attractive force between objects, although there are other effects such as frame dragging to take into account. Without mass or energy there is no bending of spacetime and thus no gravity.

 

[Chronos]

It would be pointless to talk about being 100 light years, or any other 'distance' away from the big bang. There is no space or time in the absence of a gravitational field. See http://www.astronomycafe.net/gravity/gravity.html for discussion

 

[Flatland]

How do you know that? How can you be sure? We do not have a scientific consensus that space did not exist before the start of expansion.

No one knows it's just that this is the best answer we have right now. The Big Bang was the beginning of spacetime as we know it. Some type of spacetime might have existed before the Big Bang but it certainly wouldn't be the same type that existed after, otherwise our model wouldn't break down. It certainly wouldn't be something you can stand in. I'm not sure if there is any consensus on whether spacetime existed prior to the Big Bang but I'm willing to bet that most Physicist will tell you no.

 

[texasH53D]

OP, here's my two cents though it might be worth less than that ha.
First off, from what I understand, there is no "nothingness". We cannot understand "nothingness" because we have found that "nothingness" actually has physical value. In fact "empty space" is not so empty. It is a cauldron of particles.
So, here is what I understand: when the universe was bare from galaxies, stars, planets and what have you, there were still elementary particles flying around and eventually, when particles were traveling fast enough and collided, the big bang happened and the byproduct of that was a whole bunch of other particles.
I have no idea what you may have seen or felt first as there may have been more photons given off first, or maybe more (gravitons I think their called, what gives gravity... gravity?) were given off first.
S.N; If there are particles in "nothingness" then that means the higgs field is in there too because it's what gives particles their mass right ? And if protons were there too, than so was the strong and weak nuclear forces as well right ? I am just as lost.

 

[Drakkith]

Texas, your understanding is not correct. We don't know how the universe was created, we only know that the early universe was very dense, very hot, and consisted of a sea of very energetic particles and radiation. Before this point in time we know nothing, as the math in our theories breaks down and starts giving us infinities.

See here: http://en.wikipedia.org/wiki/Chronology_of_the_universe

 

[Chalnoth]

Oh yeh! I forgot... but what about the inflation at the start of the big bang? So if gravity propagates at the speed of light and the universe is expanding faster than the speed of light, then are there some parts of space which do not have any gravity?

Saying that the universe expands faster than light is a nonsensical statement. Expansion cannot possibly be faster (or slower) than the speed of light, because expansion isn't a speed! Expansion is a rate. It's like saying that your car's engine can't revolve at faster than 60 mph: that statement doesn't make sense, because engine revolutions are measured in RPM's, which are not a speed at all.

And just as matter cannot ever outpace a light ray, due to the speed of light limitation, matter also cannot outpace the gravity it produces. So it is fundamentally impossible for matter and gravity to become somehow separated.

 

[Chalnoth]

Texas, your understanding is not correct. We don't know how the universe was created, we only know that the early universe was very dense, very hot, and consisted of a sea of very energetic particles and radiation. Before this point in time we know nothing, as the math in our theories breaks down and starts giving us infinities.

See here: http://en.wikipedia.org/wiki/Chronology_of_the_universe

"Was created" is just bad language. Formed is more neutral word.

And I would say it is just plain false that we know nothing. We don't know specifically what happened yet, and certainly don't know that much. But that doesn't mean we know nothing.

 

[Deleted member 498135]

"Was created" is just bad language. Formed is more neutral word.

And I would say it is just plain false that we know nothing. We don't know specifically what happened yet, and certainly don't know that much. But that doesn't mean we know nothing.

True, a lot of people ask me that if science is right, then explain how the world was created. I say that "you don't have to believe in it, but science is explaining things new everyday, unanswered questions will become answers" (this is after me explaining the Big Bang theory). They don't understand that science is progressing, not to be offensive or rude but don't you think it's more reasonable to believe what science says and explains rather than philosophy and *other beliefs***?

 

[Enigman]

An off-topic and possibly naive question:
Doesn't the big bounce model violate the 2nd law of thermodynamics? Or does it not matter because the 2nd is largely a statistical law?

 

[Chalnoth]

An off-topic and possibly naive question:
Doesn't the big bounce model violate the 2nd law of thermodynamics? Or does it not matter because the 2nd is largely a statistical law?

It certainly seems to violate the second law to me. The proponents of the more recent versions of the loop quantum gravity-based bounce models claim that it doesn't violate the second law of thermodynamics, but I remain incredibly skeptical. The only way in which I've heard it explained clearly sounded more like avoiding the problem rather than solving it.

 

[MathJakob]

Saying that the universe expands faster than light is a nonsensical statement. Expansion cannot possibly be faster (or slower) than the speed of light, because expansion isn't a speed! Expansion is a rate. It's like saying that your car's engine can't revolve at faster than 60 mph: that statement doesn't make sense, because engine revolutions are measured in RPM's, which are not a speed at all.

And just as matter cannot ever outpace a light ray, due to the speed of light limitation, matter also cannot outpace the gravity it produces. So it is fundamentally impossible for matter and gravity to become somehow separated.

Maybe I misunderstood but I thought the current understanding was that the universe is expanding and the rate is increasing more and more and then universe can expand faster than the speed of light withou violating relativity?

So if the rate gets faster and faster, will it not eventually be expanding at a rate greater than the speed of light? I hope I'm making sense.

 

[Chalnoth]

Maybe I misunderstood but I thought the current understanding was that the universe is expanding and the rate is increasing more and more and then universe can expand faster than the speed of light withou violating relativity?

So if the rate gets faster and faster, will it not eventually be expanding at a rate greater than the speed of light? I hope I'm making sense.

A rate is not a speed. Rate is inverse time (think of it as a percent that our universe expands every second...for reference it's 0.0000000000000002% per second, or about 7% per billion years). It is simply not possible to compare a rate to a speed, as the units of speed are distance per time.

Saying, "The universe is expanding faster than the speed of light," is rather like saying, "The length of that road is faster than 15 miles per hour." The sentence doesn't even make sense.

 

[marcus]

An off-topic and possibly naive question:
Doesn't the big bounce model violate the 2nd law of thermodynamics? Or does it not matter because the 2nd is largely a statistical law?

Several explanations have been given, one I like is based partly on the observation that you cannot state the 2nd Law without the distinction of macro and micro degrees of freedom and what defines a macroscopic degree of freedom is what affects a second system. The macro degrees of freedom are what appear in the interaction Lagrangian.
They are what matter to the second system. And BTW the primitive ideas of order and disorder also depend on what matters to the second system, with which the first is interacting.

There was some discussion of that in Rovelli's recent FQXi essay contest entry Relative Information at the Foundation of Physics, which as i recall got second prize. It's a wide audience essay, just 3 pages.

When one focuses on the Loop cosmology big bounce another issue that comes to the fore is the definition of entropy of geometry i.e. entropy of the gravitational field. To date this has not been satisfactorily defined. It would play a huge role in the total entropy, the matter part would be comparatively small. How would one define the entropy of geometry at the bounce when due to quantum effects gravity is repellent?

As long as gravity is universally attractive the gravitational field tends to become CLUMPY. Density and curvature tends to accumulate in knots and clusters. So a clumpy geometry is the HIGH ENTROPY one and smooth even geometry is LOW.

But as soon as gravity becomes repellent then smooth uniform geometry is HIGH entropy, because that is the direction in which things evolve.

1. Can you imagine a partition of the system which endures thru the bounce so that interaction
d.o.f. and hence entropy can be defined at all?

2. If entropy of any sort can be defined consistently thru the bounce, then what about entropy of the grav field, the geometry itself IOW? There is currently no generally accepted definition.

3. If the entropy of the geometry of the universe can be acceptably defined in a regime in which gravity is consistently attractive, then what happens at high density when according to Loop it turns temporarily repellent due to quantum corrections? This would seem to reverse the definition of entropy--turn it around 180 degrees.

So a naive interpretation of 2nd Law does indeed encounter difficulties. It's a good question to be asking Enigman! I think some interesting developments will come out of people taking a closer look at quantum gravity and thermodynamics.

Check out the fourth quarter MIP Poll! there's some new research in the area of QG and thermo.
https://www.physicsforums.com/showthread.php?t=730750

 

[marcus]

Maybe I misunderstood but I thought the current understanding was that the universe is expanding and the rate is increasing more and more and then universe can expand faster than the speed of light withou violating relativity?

So if the rate gets faster and faster, will it not eventually be expanding at a rate greater than the speed of light? I hope I'm making sense.

Basically you are making sense and it's a reasonable question to be asking MathJakob.
Notice that in a uniform pattern of distance expansion NOBODY GETS ANYWHERE, everybody just gets farther apart. Nobody is favored to catch up with anybody else, or to overtake a photon of light. Distance growth is not like ordinary motion where you get somewhere. So the relativity speed limit does not apply to it. There is no reason that distances cannot increase faster than light.

Since the speed of increase is proportional to the size of the distance, it is the very large distances that are increasing faster than light. While shorter distances grow at a barely noticeable rate. (And within a gravitationally bound structure like our galaxy, not at all.)

A good way to think of the current rate of distance growth is 1/144 of a percent per million years

According to the standard cosmic model that nearly all cosmologists use that percentage growth rate is slowly declining towards about 1/173% per million years, where it is slated level off and not decline further.

Since the percentage rate has become nearly constant (slow decline from 1/144 down to 1/173 is not much change) if you watch a particular distance (say between two clusters of galaxies) you would see ALMOST exponential growth of that distance. Like money deposited at a bank at a small but nearly constant percentage rate of interest. that's the "acceleration" they talk about. It is not very dramatic.

 

[timmdeeg]

Since the percentage rate has become nearly constant (slow decline from 1/144 down to 1/173 is not much change) if you watch a particular distance (say between two clusters of galaxies) you would see ALMOST exponential growth of that distance.

I am sceptical regarding this conclusion, as the matter density today is about 25% of the total energy density. The universe will approach an exponential expansion asymptotically once the percentage of matter density goes to zero, hereby assuming that the dark energy acts like a cosmological constant. Perhaps there are estimates, when this will happen.

 

[Chalnoth]

I am sceptical regarding this conclusion, as the matter density today is about 25% of the total energy density. The universe will approach an exponential expansion asymptotically once the percentage of matter density goes to zero, hereby assuming that the dark energy acts like a cosmological constant. Perhaps there are estimates, when this will happen.

Once the matter density goes to zero, the expansion will be exponential, no asymptotic about it.

What is asymptotic is the approach of the matter density to zero. The matter density is already low enough that the current and future expansion is pretty close to exponential.

 

[marcus]

I am sceptical regarding this conclusion, as the matter density today is about 25% of the total energy density. The universe will approach an exponential expansion ...

I'm not sure what conclusion you find dubious, Tim. I'm saying that right now we have almost exponential distance growth at around 1/144% per My
And eventually in future we will have exponential growth at 1/173% per My (according to standard cosmic model).

Maybe the the word "almost" is too vague for you. It is vague! I think you would like to see a TIMETABLE for the decline in percentage growth rate from 1/144 to 1/173 and that is easy to supply. Just google "lightcone cosmological calculator" and look at the column labeled "R" for Hubble radius.
As that increases from 14.4 to 17.3 the percentage rate declines accordingly.

You can compare that with the "T" column which gives the time since start of expansion, i.e. age.

To get better time resolution, first click "set sample chart range" and then "calculate"

that will give a longer table with more gradual increase from today's 14.4 to eventual 17.3.

It also gives a substantial chunk of the past. You can see for instance that the distance growth rate was approximately 1% per My back in the year 67 million. that is what the first row of the table says (if you have pressed "set sample chart range")

If googling does not work, here is the link:
http://www.einsteins-theory-of-relativity-4engineers.com/LightCone7/LightCone.html

I also keep the link in my signature, it's handy for a LOT of purposes. You get to set the parameters of the table.

 

[timmdeeg]

I'm not sure what conclusion you find dubious, Tim. I'm saying that right now we have almost exponential distance growth at around 1/144% per My
And eventually in future we will have exponential growth at 1/173% per My (according to standard cosmic model).

Maybe the the word "almost" is too vague for you. It is vague! I think you would like to see a TIMETABLE for the decline in percentage growth rate from 1/144 to 1/173 and that is easy to supply. Just google "lightcone cosmological calculator" and look at the column labeled "R" for Hubble radius.
As that increases from 14.4 to 17.3 the percentage rate declines accordingly.

Thanks marcus and congratulation to you and Mordred, this table is very helpful. I haven't realized it till now and for sure will be busy with it from now on. And I agree regarding the development of 1/R , we are now already relatively close to exponential expansion, though it will take another 78 Gy to reach R = 17.2999, corresponding to an almost exponential expansion. Hereby I use 'almost' only in the sense to not hide that the approach is asymptotic.

 

[timmdeeg]

Once the matter density goes to zero, the expansion will be exponential, no asymptotic about it.

What is asymptotic is the approach of the matter density to zero.

It seems curious. "Gegen Null gehen" translated into English means "approaching zero", so, seems different from "goes to zero", as I used it wrongly by translating directly. I appreciate your comment.